Aid to striking an electric arc



p 19, 1967 J. o. PETERSON PAID TO STRIKINCI AN ELECTRIC ARC Filed Dec. 1. 1964 INVENTOR.

JOHN D. PETERSON BY A 21 j ATTORNEYS United States Patent 01 3,343,033 AID T STRIKING AN ELECTRIC ARC John David Peterson, Burlington, Mass., assignor to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Dec. 1, 1964, Ser. No. 415,010 9 Claims. (Cl. 315111) ABSTRACT OF THE DISCLOSURE The invention relates to a starting mechanism for electric are devices using a radio frequency power source. Typically, two or more electrodes of an electric arc device are situated in a spaced relationship. Typically, a dielectric spacer is positioned between the electrodes to maintain the separation. In this invention, the spacer is coated with an electrical conducting material in such a way that the spacer remains an insulator to the principal are power supply but greatly reduces the impedance between the electrodes to a radio frequency power source coupled between the electrodes. This arrangement provides a quick, eflicient, very reliable starting circuit for electric are devices.

This invention relates to an aid to striking an electric arc, and more particularly a concept for facilitating the striking of an electric are using high-frequency electrical energy.

One of the more popular methods used to initiate and strike an electric are between spaced electrodes is to ionize a working fluid between the spaced electrodes by bridging the arc gap between the spaced electrodes with a highfrequency electrical spark discharge.

One important limitation of this method is that the arc gap between the spaced electrodes may differ for starting purposes and for normal running conditions. This problem is present in electric arc plasma generators of the type used in commerce to spray materials on substrates or to cut through metals. The recommended operating arc gap spacing is very often larger than the optimum arc gap ignition spacing. As a result, initiating and striking electric arcs with conventional high-frequency spark discharge equipment becomes unreliable unless the arc gap spacing is first adjusted for optimum starting and then adjusted for optimum operation.

It is an object of this invention to provide a concept whereby an electric arc may be initiated and struck be tween spaced electrodes in a simple and facile manner using high-frequency electric power without the necessity of adjusting the spacing between the electrodes.

It is another object of the invention to provide an aid for striking an electric are between two electrodes having a fixed, predetermined spacing by providing a second predetermined spacing which is a low-resistance path to highfrequency electrical energy, but a high-resistance path to the normal operating power supply.

It is yet another object of the invention to provide an aid to starting an electric are between two spaced elec trodes having a predetermined spacing by providing passive means in a second predetermined spacing which is nominally larger than the arc gap spacing, the passive means providing a preferred alternate path for a highfrequency electrical power source.

In accordance with the invention, an aid to an electric arc device comprises a first electrode and a second electrode spaced from the first electrode by a first predetermined arc gap spacing. There is also provided a second predetermined spacing, geometrically, longer than the arc gap spacing.

A normally insulating means, such as a ceramic sleeve, is placed in the second predetermined spacing. The insulating means has a remote and a proximate surface, the latter defining a passage in fluid communication with the arc gap spacing. The electric arc device also includes a means for supplying a working fluid to said passage for passing the working fluid between the electrodes.

Preferably, the remote surface of the insulating means is partially coated with an electrical conducting material such as aluminum or silver paint whereby a portion of the surface will conduct electricity and a second portion of the surface remains an insulator. The conducting and insulating portions are in series, and their combined length bridges the second predetermined spacing. The length of the insulating portion of the remote surface is constructed to be less than the arc gap spacing.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a sectional schematic representation of a typical plasma-generating device;

FIGURE 2 is a section taken along lines 2-2; and

FIGURE 3 depicts an insulating sleeve used in the FIGURE 1 device.

Referring to FIGURE 1 of the drawings, there is shown a schematic cross section of a typical plasma-generating device 10 containing a first electrode 11 spaced from a nozzle electrode 12 by a first predetermined arc gap spacing 15. The electrode 11 is a pencil-shaped electrode having a terminal end 16 extending into the nozzle electrode 12, as shown. The above-described construction is typical of many such devices.

The electrodes 11 and 12 are also separated by a second predetermined spacing d in which is placed a normally electrical insulating means 13. The insulating means 13 is preferably formed in the shape of a sleeve, as shown. Although sleeve 13 may be formed from any conventional electrical nonconductor, it is preferably made of alumina or ROSITE, an asbestos based material, both of which are porous to high-frequency electrical energy.

Referring to FIGURES 2 and 3 of the drawings, it is seen that the sleeve 13 contains a remote surface 18 and an interior or proximate surface 19. The latter (see FIG- URE 1) forms a passage 17 for supplying a working fluid, which enters through aperture 21, to the arc gap spacing 15 between the electrodes 11 and 12.

The remote surface 18 of the sleeve 13 includes a coating 14. The coating 14 is an electrical conducting material and is preferably silver or aluminum paint. It will be noted, in particular, with respect to FIGURE 3 that the coating 14 does not cover the entire length of the surface 18 and that, in particular, portions of the surface 18, designated 22, are deliberately not coated, and thereby remain electrical insulating portions. The combined length of the electrical conducting and electrically insulating portions 14 and 22 equals the second predetermined spacmg The bushing 11a in FIGURE 1 is constructed of metal and provides a support for the electrode 11. In effect, the bushing 11a is an extension of the electrode 11, and the contact between the two parts forms an excellent electrical conducting path.

In a traditional fashion, electrical power is supplied between the electrode 11 and the nozzle electrode 12. As indicated in FIGURE 1, the electrical power supply 23 is a combination of high frequency and direct current supplies such as a commercial welding electrical supply.

The high frequency imparts a potential difference between the electrode 11 and the nozzle electrode 12 which varies at a high-frequency rate of several thousand cycles per second. The DC. power supply is a low voltage, typically in the order of 100 volts or less and high current, typically in the order of 1,000 amperes, supply means. Power supply means 23 may be a conventional welding electrical supply.

In the course of a normal operating cycle, a working fluid is fed through aperture 21 into the passage 17 and then between the arc gap spacing 15 between the electrodes 11 and 12. In order to initiate or strike an arc, the working gas must first be ionized and thereby converted from a nonconducting medium to an electrical conducting medium. To do this, high-frequency power is first coupled to electrodes 11 and 12. Since it is desired to maintain the arc gap spacing 15 between electrodes 11 and 12 fixed, and further since it is assumed that, with this spacing, some difliculty will be encountered in starting or initiating an are, an alternate starting circuit has been provided through the specially constructed sleeve 13.

One of the characteristic properties of a high-frequency energy is its ability to spark across or bridge air spaces and porous insulators with comparative ease, providing there is a reasonable relationship between the high-frequency voltage and the spacing that is to be traversed. In this particular concept, the high-frequency electrical power is made to pass from the nozzle electrode 12 to the electrical conducting coating 14 across a space which has been designated 24, through the electrical conducting coating 14 across a space designated 26 to the bushing 11a and thence to the pencil electrode 11. The total length of the spaces 24 and 26 is appreciably less than the length of the air gap space 15. In the course of passing from the nozzle electrode 12 to the electrode 11, the highfrequency electrical energy (spark) ionizes the working fluid present in the spaces 24 and 26 and in the passage 17. As the ionized working fluid passes between the electrodes 11 and 12 in the arc gap space 15, it forms a conductive path of sufliciently low resistance to permit the flow of low-voltage, high-current power between the electrodes, creating an arc. The low-voltage, high-cub rent power is supplied from the DC. portion of the power supply means.

Although the previous D.C. energy for the arc, it is quite may also be used.

The spaces 24 and 26 may be constructed by making the length of the sleeve 13 slightly smaller than the separation between the nozzle electrode 12 and the bushi-ng 11a so as to allow working fluid to flow into these spaces easily. This construction would be necessary if a nonporous sleeve were used. As a practical matter, the sleeve 13 need not be constructed in this manner, since alumina and ROSITE, previously mentioned as the most desirable materials, are extremely porous to the high-frequency electrical energy. Thus, the energy can be made to flow through the wall of the sleeve 13 as well as over one surface thereof. This is particularly significant in the area of the space 24 in the structure shown in FIGURE 1, where the shortest distance between the coating 14 and the nozzle electrode 12 is through the sleeve 13.

When the arc is initiated in the nozzle electrode, the high-frequency energy is turned off. Since, in general, the arc is supplied by a low voltage D.C. power source, the nonelectrical conducting portions 22 of the remote surface 18 of the sleeve 13 act as an adequate insulating barrier for preventing a flow of current from the nozzle electrode 12 to the bushing 11a and electrode 11 through the alternatepath taken by the high-frequency energy.

In summary, the construction described provides a passive system wherein high-frequency energy is provided a comparatively low-resistance path for ionizing discussion has been limited to clear that AC. energy a working fluid for creating a low-resistance conductive path between the principal electrodes 11 and 12 in the vicinity of the arc gap spacing 15. Additionally, this same passive starting circuit is designed to prevent the passage of low-voltage, high-current power from the DC. portion of the power supply means.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims:

What is claimed is:

1. In an electric arc device containing at least two spaced electrodes having a predetermined arc gap spacing and means for coupling said electrodes to high-frequency starting power supply means and normal operating power supply means, a spacer separating the electrodes by a second predetermined spacing longer than said are gap spacing, said spacer containing at least one normally insulating portion in series with at least one electrical conducting portion, the combined lengths of said normally insulating and electrical conducting portions bridging said second predetermined spacing between said electrodes, said normally insulating portion having a length less than said arc gap spacing.

2. In an electric arc device containing at least two spaced electrodes having a predetermined arc gap spacing and means for coupling said electrodes to high-frequency starting power supply means and normal operating power supply means, a spacer separating the electrodes by a second predetermined spacing longer than said arc gap spacing, said spacer containing at least one porous, normally insulating portion in series with at least one electrical conducting portion, the combined lengths of said normally insulating and electrical conducting portions bridging said second predetermined spacing between said electrodes, said porous, normally insulating portion having a length less than said are gap spacing.

3. In an electric arc device containing at least tWo spaced electrodes having a predetermined arc gap spacing and means for coupling said electrodes to high-frequency starting power supply means and normal operating power supply means, a spacer separating the electrodes by a second predetermined spacing longer than said are gap spacing, said spacer containing two normally insulating spaced portions in series with an intermediate electrical conducting portion, the combined lengths of said normally insulating and electrical conducting portions bridging said second predetermined spacing between said electrodes, said normally insulating portions having a com bined length less than said arc gap spacing.

4. In an electric arc device containing a first electrode, a second electrode spaced from said first electrode by a first predetermined arc gap spacing, and means for supplying high-frequency starting and normal operating electrical power to said electrodes:

(a) a normally insulating sleeve, having an exterior surface, positioned between said first electrode and said second electrode, the height of said sleeve being longer than said arc gap spacing; and

(b) electrical conducting means overlying said exterior surface defining an electrical conducting portion and a normally insulating portion on said exterior surface, the length of the normally insulating portion being less than said are gap spacing.

5. An electric arc device comprising:

(a) a nozzle electrode;

(b) a pencil electrode having a terminal end protruding into said nozzle, said terminal end being spaced from said nozzle by a first predetermined arc gap spacing, said pencil electrode also being spaced from said nozzle electrode by a second predetermined spacing which is longer than said are gap spacing;

(c) a normally insulating sleeve, having an exterior surface, positioned between the nozzle electrode and said pencil electrode in said second predetermined spacing, said pencil electrode passing through said sleeve into said nozzle; and

(d) an electrically conducting means overlying said exterior surface defining an electrically conducting portion and a normally insulating portion of said exterior surface, the length of the normally insulating surface being less than said are gap spacing.

6. An electrical arc device as defined in claim 5 in which said sleeve is porous to high-frequency electrical energy.

7. An electrical arc device as defined in claim 5 in which said electrically conducting portion comprises a metallic coating on said sleeve.

8. An electric arc device comprising:

(a) a first electrode;

(b) a second electrode spaced from said first electrode 20 by a first predetermined arc gap spacing and a second predetermined spacing longer than said are gap spacing;

(c) a normally insulating means bridging said second predetermined spacing, said insulating means having a remote and a proximate surface, the latter defining a passage in fluid communication with said arc gap spacing;

10 which said normally insulating means is porous to highfrequency electrical energy.

References Cited UNITED STATES PATENTS 3,143,647 8/1964 Kari-Georg Gunther 315-111 3,151,259 9/1964 Gloersen et al. 315-111 3,231,778 1/1966 Allgaier 315-411 FOREIGN PATENTS 671,404 10/ 1963 Canada. 1,155,863 10/1963 Germany. 809,323 7/1951 Germany.

25 JOHN W. HUCKERT, Primary Examiner.

JAMES D. KALLAM, Examiner.

A. J. JAMES, Assistant Examiner. 

1. IN AN ELECTRIC ARC DEVICE CONTAINING AT LEAST TWO SPACED ELECTRODES HAVING A PREDETERMINED ARC GAP SPACING AND MEANS FOR COUPLING SAID ELECTRODES TO HIGH-FREQUENCY STARTING POWER SUPPLY MEANS AND NORMAL OPERATING POWER SUPPLY MEANS, A SPACER SEPARATING THE ELECTRODES BY A SECOND PREDETERMINED SPACING LONGER THAN SAID ARC GAP SPACING, SAID SPACER CONTAINING AT LEAST ONE NORMALLY INSULATING PORTION IN SERIES WITH AT LEAST ONE ELECTRICAL CONDUCTING PORTION, THE COMBINED LENGTHS OF SAID NORMALLY INSULATING AND ELECTRICAL CONDUCTING PORTIONS BRIDGING SAID SECOND PREDETERMINED SPACING BETWEEN SAID ELECTRODES, SAID NORMALLY INSULATING PORTION HAVING A LENGTH LESS THAN SAID ARC GAP SPACING. 